1. Field of the Invention
The invention pertains to the field of tensioners. More particularly, the invention pertains to chain drive tensioner spring force control mechanisms.
2. Description of Related Art
Generally, in timing chains for valve drives of internal combustion engines, camshaft chains in use for a camshaft-camshaft drive, and balancer chains, have tensioners that are used on the slack side of a chain to take up slack in the chain and to apply tension to the chain.
During operation, a piston of the tensioner presses against the chain to maintain tension in the chain. When tension in the chain increases during operation due to resonance of a chain span, a high load from the chain acts on the piston of the tensioner, causing the piston to retract into the housing of the tensioner.
Chain drive tensioner spring force is often too high for most operating conditions so that the spring force is sufficient to handle worst case operating conditions of the tensioner system. The effectiveness of the tensioner and the overall system behavior and efficiency could be improved if the tensioner spring force could be varied with operating conditions taking into account wear and stretching that occurs in the chain during the life of the chain.